import time

class Chock:
	def __init__(self):
		self.run_time = 0
		self.could_stop = False
	
	def start(self):
		self.could_stop = True
		self.start_time = time.clock()
	
	def stop(self):
		self.stop_time = time.clock()
		self.run_time = self.start_time - self.stop_time
		self.could_stop = False
	
	def start_again(self):
		self.could_stop = True
	
	def __str__(self):
		return self.run_time
	
	__repr__ = __str__